In filariasis the infectivity of the appropriate mosquito vector is not consistent with the microfilarial density of the host. The reason may be attributed such factors as the time of microfilarial appearance in the peripheral blood of the host, the time of maximum biting activity of the arthropod vector, or the morphological adaptation of the feeding mechanism of the vector. However, it is quite puzzling to see why the number of microfilariae taken up by mosquitoes is subjected such a great variation, even though the same batch of mosquitoes are fed on the same filarial host under same laboratory conditions. The experiment was designed to observe more detail aspect of this relation. Adult Aedes togoi (Theobald, 1907) mosquitoes were reared from egg rafes colonized in an insectary. Animals used were Taiwan monkeys, Macaca cyclopsis which had been artificially infected with Wucheria malayi. The animals showed the microfilarial counts as low as nil to ten per slide of 20 cmm3 of blood, which seem to be rather fortunate for this kind of work. The microfilarial density of each animal was counted by taking each ten smears of 20 cmm(3) of peripheral blood the ear lobes before and after mosquito bite. Feeding were done in two occations, during 1600-1630 and 1900-1930 hours of the same day. The monkeys were immobilized and a rayon cage, housed 100 female mosquitoes for two days starvation, was exposed to the shaved abdomen of each animal. Fully engorged mosquitoes were transferred to a square rearing cage, which was later placed in the insectary, where kept temperature of 23-27degree C and relative humidity of 80-85 per cent. It was found that filarial larvae of the mosquito body usually develop to the third or infective stage in about 10 days after blood meal under these conditions. Daily dissections were made of these mosquitoes, either living or dead, after one week of rearing. Analysing of the result, the following conclusion was made. The rate and intensity of infection in mosquitoes are not directly related to the blood counts of microfilariae of the host animals. This is perhaps due to fluctuations of microbial outflow in the peripheral blood of individual animals. The reason of this would be no doubt due to a patch type of microfilarial distribution in the host blood.

The authors carried out histochemical studies on Clonorchis sinensis, especially, histochemical demonstration of carbonic anhydrase activity. Kurada's method was applied for the histochemicl staining in this study. The result obtained were summerized as follows : Carbonic anhydrase activity was intensely positive in oral sucker cells, reticular tissue cells, epithelium of the intestine and testes, more or less intensely positive in vitelline gland cells and yolk of eggs as well.

The histochemical study, especially the demonstration of alkaline phosphatase and acid phosphatase was carried out in order to differentiate ascarides of human and pigs. The experimental material were obtained from naturally contaminated men and pigs. As the histochemical staining methods the Gomori's was applied for acid phosphatase and Takeuchi and Takami's for alkaline phosphatase. The results obtained were summerized as follows : In the pig's ascarides, alkaline phosphatase was richly found in the subcuticular tissue, lateral line, median line, strial zone and epithelial cells of the intestine, epithelial cell and basal membrane of the ovary, the same part of the uterus and also in eggs. Acid phosphatase in the pig's ascarides were distributed in the same part as alkaline phosphatase. It, however, was darker brown in the soft tissue of the lateral line, epithelium of excretory canal, median bundle, whole zone of the intestine and intestinal contents. In the human ascarides, the alkaline phosphatase was distributed in the testes and the parts where the acid phosphatase was found in the pig ascarides. The acid phosphatase in the human ascarides was demonstrated in the subcuticular tissue, soft tissue of lateral line, epithelium of excretory cells, strial zone, transparent zone, granular zone and epithelial zone of esophagus and intestine, ovary, ova in the uterus, epithelial cell and basal membrane of the uterus and in testes. In the pig's ascarides, the area of distribution of alkaline phosphatase was restricted, but that of acid phosphatase was wider. In human ascarides, the area of distribution of alkaline phosphatase and acid phosphatase was not significantly different, but in some part showed slight difference. Above mentioned finding suggest that the distribution of phosphatase could be utilized for the differentiation of ascarides of human and pig.

The phamacological and anthelmintic action of Lysimachia clethroides were examined. Upon examining the action of water, ether, alcohol and acetone extrcts of the root on smooth muscle, it was found that the active principle was weakened by heating. Water and ether extracts inhibited the dehydrogenase of the worm. In 50 percent of 8 areas studied, Taenia were completely eliminated with 2.5-4.0 gm doses of the ether extracts, and no toxic effect was observed by the administration of the above-mentioned doses.

The localization of Giardia muris was determined in 8 Giardia-infected laboratory mice that were fed on a normal diet. The average total length of small intestine of the mice was 38.3 cm. Among 8 sections (to divide into 8 part from pylorus to cecal junction :Sect. I, Sect. II, ...... Sect. VIII), the optimum habitat ranged Sect. IV to Sect. V(from 14.5 cm to 24.4 cm posterior to the pylorus. Distribution rate of Giardia muris in posterior part of small intestine was higher than that in anterior part. The bile duct of 8 mice were examined, but no Giardia was found. The cyst of Giardia muris were found at the part posterior to the Sect. VII. The result of a comparison between varying average body length and body breadth of Giardia muris drawn at random from different part of small intestine of 5 laboratory mice was as follows : Maximum average dimension of the body length of the trophozoite was found at the part of Sect. IV and minimum average value was observed at the part of Sect. VIII. On average dimension of body length of the trophozoite, no significant difference was obtained among the parasites at Sect. II, Sect. IV, Sect. VI, but significant small dimension value was observed aat Sect. VIII. Coincidental figures on the part where the maximum distribution rate was shown and the part where the maximum average dimension of the body length of the trophozoite were considered as indicating the optimum site of the parasite.

Mice were infected by feeding the embryonated eggs of Toxocara canis and Ascaris lumbricoides. Each mouse was killed daily for a week and then at several days interval after infection and the distribution of larvae in the various tissues of mice was investigated after the macerating the tissues and digesting with artificial gastric juice. It was confirmed that the migratory behaviour of larvae of T. canis and A. lumbricoides is referred to as the somatic and tracheal type of migration in the mice respectively. Toxocara larvae were found in the carcass on the third day after infection and in the brain after the sixth day of infection. From the thirty-fifth day to the seventy-sixth day after infection, Toxocara larvae were not found in the tissues of mice except in the carcass and brain and they did not develop further than the second-stage larvae. The size of Ascaris larvae, from the embryonated eggs was 0.228-0.271 mm length by 0.010-0.013 mm width and in the third day of infection the size of larvae was 0.271-0.343 mm length by 0.017-0.020 mm width. Between the fifth and tenth day after infection, lavrae molted twice in the lungs and grew to the fouth-stage larvae; 1.357-2.0 mm by 0.034-0.071 mm. These larvae migrated to the intestinal canal after the tenth day of infection and disappeared from the mouse after the twenty-fifth day of infection. No larvae were found in the carcass and brain. The inflammatory reactions in the tissues of infected mice were also observed.

Ever since the first intermediate host of Clonorchis sinensis was identified with Bulimus striatulus, it has been place to an important position in epidemics. One way to prevent Clonorchis sinensis is to exterminate Bulimus, which is itself the first intermediate host and there by to separate the life cycle of Clonorchis. In killing B. striatulus, nicotine sulfate and lindane have been chosen from insecticides which are widely used in farming areas. And then nicotine sulfate and lindane have been used to check their effectiveness in killing B. striatulus. In this experiment, the resistance of cercaria which parasites to B. striatulus has also been studied. Dipping method was used in the study. Nicotine sulfate and lindane have been used to check the mortality effect. Nicotine sulfate was used to check percentage of mortality in varied times. The existance of cercaria was tried only in nicotine sulfate. In the experiment of mortality effect of insecticides to B. striatulus and cercaria, the difference in killing rate and the resistance in different concentration and different length of time have been researched. It resulted as following: In the experiment with nicotine sulfate, the mortality increased with thicker concentration in the constant length of time. When compared the necessary liquid of nicotine sulfate and lindane in LD 50, nicotine sulfate was less used than lindane, but the mortality proved high. In the treatment to the same concentration of nicotine sulfate in different length of time, it proved that the longer period showed higher mortality. The mortality time required in LD 90 of nicotine sulfate was dependent on the concentration. And thicker concentration showed quicker effect. In the resistance of cercaria and B. striatulus to nicotine sulfate, the resistance of cercaria was proved to be stronger than that of B. striatulus.